1. Field of the Invention
The present invention relates to a flexible-film expandable gate, and in particular, to a flexible-film expandable gate which is disposed in a pipeline, and which adjusts the cross-sectional area of the flow path within the pipeline by being inflated (expanded) and collapsed (contracted) due to the supply and discharge of a fluid.
2. Description of the Related Art
There has conventionally been known the technique of placing a flexible-film expandable gate, which is structured by a flexible-film body, within a pipeline of waterworks or the like, and opening and closing the pipeline by inflating and collapsing the flexible-film body by the supply and discharge of a fluid (a gas or a liquid) into and from the flexible-film body.
For example, the gate for a pipeline shown in FIG. 10 (refer to Japanese Patent Application Laid-Open (JP-A) No. 2002-88746) has a pad 114 provided on the floor surface of a pipeline 112, and a film body 116 provided on the pad 114. An upper film 118 and a lower film 120, which structure the film body 116, are mounted by fixing means to the pad 114 in a sealed state. Air is supplied into the space between the upper film 118 and the lower film 120, such that the upper film 118 is inflated.
In a flexible-film expandable gate having such a structure, when, for example, the diameter of the pipeline 112 is large, the radius of curvature of the upper film 118, in the state in which the upper film 118 is inflated and tightly contacts the upper wall surface of the pipeline 112, is large. Further, when damming-up a fluid of a high water level for example, high fluid pressure reaches the upper film 118, and the pressure within the film body 116 increases.
Here, it is generally known that the tension acting on the film body is the product of the internal pressure of the film body and the radius of curvature of the film body when inflated. Therefore, in a case in which the pipeline has a large diameter and a fluid of a high water level is dammed-up, a film body having high strength, i.e., high rigidity, is needed in order to be able to withstand the high tension.
However, when a highly-rigid film body is used in order to improve the durability, the elongation of the film body when inflated is poor. Therefore, it is difficult to completely block-up the pipeline.